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Scientists Miller and Schuster are part of an international project to increase genetic diversity among the vanishing Tasmanian devils. Schuster said the current diversity of the Tasmanian devils is even lower than that of the Tasmanian tigers before their extinction.

Genetics of extinction offers hope for the endangered

by Kristen Minogue
Jan 14, 2009


Photo courtesy of Smithsonian Archives.

These Tasmanian tigers, or thylacines, lived in the National Zoo in Washington, D.C., before the species went extinct in 1936. Scientists said they believe they analyzed genetic data from the tiger in front.

More than 70 years after the last known Tasmanian tiger died, researchers say they have unlocked a new clue to its extinction – and a way to stop a similar fate from befalling its close genetic relative, the Tasmanian devil, a small mammal that resembles a furry pig. 

The Tasmanian tiger, a striped animal that’s actually more closely related to the kangaroo, was declared extinct in 1936. During the decades before its demise, European hunters dramatically lowered the population. American and European scientists who published their results Tuesday in Genome Research say hunting drained the gene pool, creating a genetic “bottleneck” that left the already dwindling population even more vulnerable because its surviving members were too genetically similar. 

Genetic diversity refers to any genetic differences in members of a species: differences in height, color, or the ability to resist disease.

“If a species doesn’t have sufficient diversity, they’re not able to adapt to changing environments very easily,” said Jeffrey Doering, biology department chair at Loyola University Chicago who did not take part in the study. Too much similarity can spell death for an entire species.

Researchers examined genetic data from the hair of two separate Tasmanian tigers that died more than a century ago, one in the National Zoo in Washington, D.C., and one in the London Zoo.

The scientists analyzed more than 15,000 nucleotides – tiny molecules that form the building blocks of DNA. When they compared data from both animals, only five of the 15,000-plus nucleotides were different, indicating "a loss of genetic diversity, which is exactly what we find shortly before they go extinct,” said Stephan Schuster of Pennsylvania State University, one of the study’s co-authors.

Schuster and his colleague Webb Miller, who also worked on the study, said they are now trying to apply that lesson in an effort to save the vanishing Tasmanian devils.

The two scientists are part of a project to increase genetic diversity among Tasmanian devils before they too disappear. The animals once flourished across Australia, but now are found only on Australia's island state of Tasmania.

The project, funded by the San Francisco-based Gordon and Betty Moore Foundation for conservation research, allows scientists to research the genes of existing devils. They then use the information to form “breeding groups” that maximize genetic diversity.

“We’re going to suggest sets of animals that we think retain the full diversity,” said Miller.

Loyola's Doering said while raising a population’s genetic diversity is easier said than done, Schuster and Miller’s method is reasonable.

Schuster said there are already 20 breeding stations underway in mainland Australia to encourage more diverse populations.

“The most amazing aspect of this project is the way that those devils are being bred, they can be released back in the wild later so they are not automatically becoming zoo animals just because they are bred in captivity,” Schuster said.

But Schuster said the right technology could make an even more radical idea possible – bringing back the Tasmanian tiger from extinction.

“It is not entirely impossible anymore,” he said.

According to Schuster, two methods could be used for resurrecting a dead species.

The first involves putting the DNA of a dead species into the egg of a living species. The newly-formed embryo is then placed inside a surrogate mother to be delivered normally.

This method, called somatic cell nuclear transfer, is used by some farmers to clone cows.

“This aspect is not science fiction,” said Schuster. “This is what’s happening today.”

But that method only works if the dead species has a living relative genetically close enough, and according to Schuster, the Tasmanian tiger doesn’t.

Method number two would involve using synthetic biology to piece together DNA. Biologist Craig Venter, who made headlines in early 2008 for stitching artificial DNA into bacteria, is taking steps toward creating the first synthetic bacteria. Schuster said he believes it might be possible to do the same for mammals like the Tasmanian tiger in the future.

Miller said he wants to keep the focus on saving species before they go extinct.

“I don’t want people thinking, we’ll just freeze one of these guys and if the species dies out and the habitat is all destroyed, who cares, because we can always bring them back,” he said. “That’s a bad way to think about it.”

“We want to study the biology of extinction and to apply the lessons learned directly to endangered species,” Schuster said. “This is why we are doing it, and not to resurrect Jurassic Park.”